A hydraulically-assisted rack and pinion steering gear includes a steering rack, a pinion gear in mesh with the rack, and a hydraulic fluid control valve. The rack is movable longitudinally, and is connected at its opposite ends to a vehicle steering linkage. When the rack moves, it actuates the steering linkage to effect steering movement of an associated pair of steerable vehicle wheels.
Such a steering gear includes a housing which contains the rack, the pinion gear, and the valve. The rack extends through a horizontal section of the housing. The valve is contained in a tower section of the housing which projects upward from the horizontal section.
The horizontal section of the housing includes a hydraulic fluid power cylinder. A piston in the power cylinder is fixed to the rack. The valve cooperates with the pinion gear to control the hydraulic fluid pressure in the power cylinder in response to steering input from an operator of the vehicle. This causes the piston, and hence the rack, to move in response to the steering input so that the vehicle wheels are steered accordingly.
An example of a prior art steering gear is shown partially in FIG. 1. The steering gear 10 of FIG. 1 has a horizontal housing section 12 in which a steering rack 14 is supported for movement back and forth along a longitudinal axis 15. The horizontal housing section 12 is defined in part by a hydraulic fluid power cylinder 16, and in part by a mounting structure 18. The rack 14 projects longitudinally outward from the horizontal housing section 12 in a direction extending from left to right, as viewed in FIG. 1. An outer end portion (not shown) of the rack 14 is connectable with a vehicle steering linkage in a known manner.
A cylindrical body portion 20 of the mounting structure 18 is received over the power cylinder 16 in an interference fit with the power cylinder 16. A radially-projecting bracket portion 22 of the mounting structure 18 defines a bore 24. The bore 24 receives a bushing which, in turn, receives a fastener structure that fastens the steering gear 10 to a load-bearing structural part of a vehicle.
Other parts of the steering gear 10 that are shown in FIG. 1 include a seal carrier 30 and a lock ring 32. The seal carrier 30 is an annular structure extending into the power cylinder 16 concentrically between the rack 14 and the power cylinder 16. An inner end surface 34 of the seal carrier 30 defines an outer end of a variable volume hydraulic fluid chamber 36. An annular hydraulic fluid seal 38 (shown schematically) is supported on the seal carrier 30 in dynamic sealing contact with the rack 14. An O-ring seal 40 is supported by the seal carrier 30 in static sealing contact with the power cylinder 16. The lock ring 32 is received concentrically over the rack 14 in screw-threaded engagement with the body portion 20 of the mounting structure 18. The seals 38 and 40 are thus retained in their installed positions at the end of the power cylinder 16 by the seal carrier 30, the lock ring 32 and the mounting structure 18.